Impulse producing oscillator



R. B. HOFFMAN IMPULSE PRODUC ING OSC ILIJATOR Filed Nov. 23', 1942 MOOULHTOR DEVICE INVENTOR. R065 5. HOFFMHN BY Z A'I'TUHNIS'Y Patented Apr. 1, 1947 STATES Arm OFFlCE IMPULSE PRODUCING OSCILLATOR Application November 23, 1942,. Serial No. 466,561

8 Claims. 1 Ellis invention relates to radio systems and more particularly to generation of impulses.

One of the objects of this invention is to provide a method and means for effecting impulse generation of substantially evenly-timed occurrence with respect to the application of energizing potentials, and wherein the amplitude of recurring impulses thus generated are substantially constant.

Another object of this invention is to provide an improved impulse generator wherein the efficiency of the generator as regards the amplitude of generated impulses is greatly improved over similar systems heretofore proposed.

It has been observed that an ultra high frequency oscillator whose anode energizing potential is momentarily supplied from a pulse modulator so that the oscillator normally has no anode voltage and is only momentarily energized for a few microseconds out of each millisecond, yields impulses of varying amplitude and. the wave fronts thereof are not timed evenly with respect to the wave fronts of the anode energizing potentials. Prior to the developlment of the arrangement described in copending application of Norman H. Young, Jr., Serial No. 452,901, filed July 30, 1942, anode potentials applied to an oscillator operated merely to bring the oscillator from a point of substantially stable quiescent equilibrium to a point of highly unstable equilibrium but did not provide any excitation to initiate the pulse oscillations. It is believedthat the pulse oscillation is initiated after an anode potential is applied to the oscillator by the presence of random voltage due to thermal or circuit noise conditions and that the oscillation impulse buildup from a very small value in an exponential fashion. It is believed that the amplitude of random fluctuations of voltage present at the instant anode potential is supplied to the oscillator controls the point of oscillation build-up on the exponential curve. That is to'say, if the ra'ndom fluctuation should be practically nil the buildup is initiated at substantially zero value on the exponential curve. If the fluctuation voltage is of some more appreciable amplitude, the buildup, is initiated at a point further along theexponential curve and the 'resulting' ulse envelope for the same energizing potential will be larger, and the wave front thereof will occur in time relation in advance of the Wave front of a pulse envelope initiated further down the exponential curve.

In the aforementioned copending application ofTNorman H. Young, Jr., a methodand'means are disclosed to minimize the variation efiect of random voltage fluctuations present in the oscillator circuit by applying an oscillation to them-- cillator circuit. This added oscillation greatly reduces the percentage variation due to random voltage present so that upon application of an anode energizing potential, initiation of the impulse envelope is caused to occur practically inestantaneously and with substantially no'variationat a higher point on theexponential buildup curve. In accordance with my invention, I utilize the anode energizing potential pulse from the modulator to apply or initiate oscillation in the oscillator circuit at substantially the instant the potential is applied to the anode input of the oscillator. I accomplish this by simultaneously applying the anode energizing potential toa readily excitable device to excite the device to resonance, the device being tuned, conditioned and/ or so-arranged that it serves to establish an exciting Voltage in the oscillator circuit. This has a-catalyzing eiiect in that with my invention I am able to efiect consistently aquick impulse envelope build-up and one in which the ampll tude is greater for the same anode-energizing potential. The wave fronts of the impulses thus produced are caused to have substantially even time relationship with respect to the wave fronts of the anode energizing potentials.

These constant amplitude and regularly occurring impulse envelopes produced in accordance with my invention are particularly useful in time modulation communicationsystems and in radio detection systems. The time modulation communication equipment may be ofthe type generally disclosed'in U. S. Patents Nos. 2,266,401 and 2,256,336 and copending applications of Emile Labin, Serial No. 386,282, filed April 1, 1941; Serial No. 406,499, filed August 12, 1941: and Serial No. 449,595, filed July 3, 1942. Examples of radio detection systems to which my invention is applicable are disclosed in the c'opendingapplications of H. Busignies, Serial No. 381,640, filed March 4, 1941. and E. Labin,,Seria1 No. 400,259, filed Junel28, 1941.

For .a better understanding of the invention reference may be had to the'following detailed description to be read in connection with the accompanying drawings, in which;

Fig. 1 is a schematic illustration of an impulse generator in accordance withmy invention;

Fig. 2'is a view in perspective of a spark gap device, and

Fig. 3 is a graphical illustration of the im-' by the modulator 3|,

3 proved impulse generating feature of my invention.

Referring to Fig. 1, I show a radio frequency oscillator comprising two vacuum tubes l6, l2, connected in push-pull arrangement. These tubes comprise plates l4, I6, respectively, connected together by a resonant linear circuit l8; grids 20, 22 respectively, connected together by a resonant linear circuit 24; and cathodes 26, 28 respectively, connected together by a resonant linear circuit 36. The resonant linear circuits, I8, 24 and 30 may be of any known type adjustable to have an electrical length of some multiple of a one quarter wavelength, and may be tuned by known means to the frequency desired. It Will be understood, of course, that the oscillator circuit could have tank circuits of lumped inductances and capacities. For ultra high frequency operation, however, tuned resonant linear circuits are preferable.

A modulator 3| for producing high voltage pulses is connected by means of a plate lead 32 to the midpoint of the oscillator plate circuit l8. From this plate lead 32 is connected 2. variable spark gap device 34 to the remote side of which is attached a conductor 36 having a length approximately equal to one quarter of the wavelength at which the oscillator is resonant.

In Fig. 2, I show in more detail the construction of the spark gap device 34. The device comprises an insulated base 56 on which is mounted two metal binding posts 52, 56. Threaded through each of said posts are metal screws 62, 64 respectively, which carry coaxially therewith two carbon cylinders 58, 60 such that the carbons may be moved coaxially with respect to each other by manipulation of the metal screws. Metal screws 62, 64 may be held from turning by two set screws 68, 70 respectively, threaded down into the tops of their respective binding posts. Near the base of binding posts 52, 56 are cylindrical holes l2, 14 which permit the insertion of conductors. Set screws l6, 18 are threaded into the bottom of said binding posts at right angles to the conductor holes so as to hold the conductors in place.

In Fig. 3, I have indicated at 80 random voltage fluctuation which'may be present in the oscillator circuit. Without the application of the catalyzing feature of my invention, the oscillator when subjected to an anode energizing potential 82 will start to oscillate and build-up an impulse envelope such as indicated by the impulses B4 and 85 depending upon the amplitude of the random fluctuation 80 at the instant of application of the potential 82. The envelope 84 which is assumed was initiated by a low amplitude random fluctuation, is of smaller amplitude than impulse 85 which is assumed to have been initiated by a voltage fluctuation of greater amplitude.. Assuming that the line 86 represents the elfective receiving level of the impulses at a receiver, it will be observed that the Wave fronts of the two impulses 84 and 85 vary in time by an interval h. It will also be observed that the amplitude of the pulses differ by an amount :11.

According to my invention, I produce impulses whichare substantially constant in amplitude and in which the wave fronts occur at substantially the same time relation With respect to th energizing wave fronts of the energizin potentials. When the high potential pulse is produced the spark gap between the carbons 58 and 60 will break down and an arc will be formed. The are that is thus formed will excite the quarter wavelength conductor 36 and cause it to oscillate at the frequency to which it is resonant. This oscillation in the conductor 36 will be instantaneously radiated to the resonant linear circuits of the oscillator so that voltages will be induced therein thus causing radio frequency oscillations to begin immediately. This excitation radiation from the conductor 36 induces oscillation in the oscillator circuit at or immediately following the application thereto of the energizing potential 82.

While in practice, the induced oscillation appears to occur simultaneously with the application of the anode energizing potential, it is assumed for purposes of illustration that a lag of t2 occurs. It will thus appear that the radiation commences at an interval t2 (Fig. 3) after application of the wave front of the potential pulse 82 and at a voltage of V1. The spark gap distance, of course, should be adjusted to a very small value in order that breakdown will occur at the lowest possible voltage consistent with continuous operation. Thus, should impulse build-up start during interval is the catalyzing effect of the radiations from the element 36 greatly increases the amplitude of oscillations thereby causing the impulse, either 84 or 85, as the case may be, to build-up at an increased rate such as indicated at 84a and a. Assuming that the impulses 84a and 85a represent the extremes in variation of impulse generation, it will be observed that the wave fronts are substantially constant in time occurrence and that the amplitudes are substantially constant and considerably greater than those of the impulses 84 and 85.

As hereinbefore stated, pulses build-up irregu larly, depending on many factors one of which is the amplitude of random voltage present in the circuit due to random circuit noise. Due to the fact that the spark gap breaks down consistently at the same voltage, each time a pulse potential from the modulator is applied to the anode input IS, a uniformity of pulse build-up is effected. In addition, I have found that the shock excitation from conductor 36 greatly improves the efliciency of the circuit and thus produces pulses of greater amplitude, that is, greater peak power.

While I have described my invention in connection with a particular spark gap device, it will of course be realized that any suitable arrangement may be used wherein a spark excites a conductor to shock excite the resonant circuits of an oscillator. It is to be undedstood, therefore,- that the embodiment herein shown and described is made only by way of example and not as a limitation on the scope of the invention.

What I claim is:

1. The method of stabilizing the impulse generation of an oscillator having an anode input which includes the steps of developing recurring energizing potentials, applying these recurring energizing potentials to the anode input of the oscillator to effect for each energizing potential the generation of an impulse, exciting the oscillator with a second, excitation voltage by radiating energy to the oscillator, and controlling the radiation in accordance with the development of each recurring energizing potential, whereby said oscillator is excited by said excitation voltage substantially simultaneously with the application of each recurring energizing potential.

2. An impulse generator comprising an oscillator, an anode input therefor, means to apply energizing potentials to said input to initiate oscillation for production of impulses, and means readily excitable to resonance in response to application of said potentials to said input, said readily excitable means being so disposed with respect to said oscillator that radiation therefrom establishes in the circuit of said oscillator an excitation of substantial amplitude substantially simultaneously wtih the application of the energizing potential, thereby efiecting for successively applied similar potentials substantially identical impulse oscillations.

3. The generator defined in claim 2, wherein the readily excitable means includes a spark gap adapted to be quickly broken down by said potentials.

4. The generator defined in claim 2, wherein the readily excitable means includes a resonatable element of a length substantially equal to one quarter of the wavelength at which said oscillator is resonant.

5. The generator defined in claim 2, wherein the readily excitable means includes a resonatable element of a length substantially equal to one quarter of the wavelength at which said oscillator is resonant, and a spark gap adapted to be quickly broken down by said potentials.

6. An impulse generator including, in combination, an oscillator including a pair of electron discharge devices, each having an anode, a cathode and a grid, a first linear resonant circuit means connected to the anodes, a second linear resonant circuit means connected to said cathodes and a third linear resonant circuit means connected to said grids, a source of recurring energizing potentials, means applying said source to one of said linear circuits, a resonant radiating device positioned within excitable range of said linear resonant circuits, and means energizing said radiating device from said recurring potential source.

7. The combination according to claim 6, in which said last means is a spark gap.

8. The combination according to claim 6, in which said linear resonant circuit means each comprising quarter-wavelength lines, and said radiating device includes a quarter-wavelength conductor.

ROSS B. HOFFMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,695,042 Fearing Dec. 11, 1928 2,057,170 Usselman Oct. 13, 1936 

